Anchor bolts are commonly used to secure various types of machines and structures to concrete surfaces. The anchor bolts are commonly placed in position and the concrete poured so that the anchor bolt becomes imbedded in the concrete with a portion of the bolt extending above the surface of the concrete. The anchor bolt commonly has an enlarged head which is imbedded in the concrete at a depth considered sufficient to provide the strength required to hold the machine or structure in position. Once the anchor bolt has been located in the concrete it is rigid and difficult to adjust to accommodate variations in location. Also because of the rigid mounting of the bolt in the concrete, overstressing of the bolt can occur, sometimes resulting in breaking or weakening of the bolt.